RU2151386C1 - Process of observation of signals of quadrupole spin echo - Google Patents

Abstract

FIELD: radio spectrometry, study of structure of chemical compounds with use of nuclear quadruple resonance. SUBSTANCE: process involves action on sample carrying quadrupole nuclei with two radio frequency pulses with time interval τ between them and basic frequency ω_Q+Δω_Q of one of pulses and basic frequency ω_Q-Δω_Q of the other pulse, where ω_Q is resonance frequency of excited junction; Δω_Q is amount off-resonance within limits of half-width of observed line of nuclear quadrupole resonance. Signals of spin echo are recorded on resonance frequency. EFFECT: generation of additional information on structure of chemical compounds thanks to observation of signals of echo of wide lines of nuclear quadruple resonance. 2 dwg

Description

 The invention relates to the field of radio spectroscopy and can be used to study the structure and structure of chemical compounds, as well as in the development of various radiophysical and radio engineering systems and devices based on the interaction of a substance with radio frequency fields.

A known method of observing quadrupole spin echo signals, including exposing a sample containing quadrupole nuclei to two radio frequency pulses with a time interval τ between them and with a filling frequency equal to ω _Q + Δω _Q (or ω _Q -Δω _Q ), where ω _Q - the resonant frequency of the excited transition, Δω _Q is the distance from the resonant frequency within the half-width of the observed NQR line, and the registration of echo signals at the frequency ω _Q + Δω _Q (or ω _Q -Δω _Q ) [1] - D. Ya. Osokin. Pulsed spinlocking in nuclear quadrupole resonance ¹⁴ N. JETP. 1983. T. 84. N 1. S. 118-122.

 This method does not allow observing spin echo signals with a maximum amplitude (since its value decreases depending on the magnitude of the detuning), and also investigating the effect of the detuning on spectral, transition, and relaxation parameters.

There is also a method of observing quadrupole spin echo signals, including exposing a sample containing quadrupole nuclei to two radio frequency pulses with a time interval τ between them and with a filling frequency equal to the resonant frequency ω _{Q of the} excited transition, and recording echo signals at this frequency [2] - EL Hahn. Spin Echoes. Phys Rev. 1950. V 80. P. 580-584 (prototype).

 This method does not allow to investigate the effect of detuning on the spectral, transition, and relaxation parameters.

 The objective of the invention is to develop a method for observing quadrupole spin echo signals, which allows one to study the effect of detuning on spectral, transient and relaxation parameters.

This problem is solved using the essential features specified in the claims that are common with the prototype: a method for observing quadrupole spin echo signals, including exposing a sample containing quadrupole nuclei to two radio frequency pulses with a time interval τ between them, recording echo signals at the resonant frequency of the excited transition - and distinctive from the closest analogue essential features: setting the frequency of filling of one of the pulses of equal ω _Q + Δω _Q, frequency and filled with other a pulse equal ω _Q -Δω _Q, where ω _Q - resonant frequency excited transition, and Δω _Q - detuning of the resonant frequency within the half-width NQR observed line. Moreover, radio frequency pulses with such filling frequencies are supplied in various ways.

 The following discloses the existence of a causal relationship between the totality of the essential features of the claimed invention and the achieved result.

Firstly, a method is proposed for observing quadrupole spin echo signals, including exposure to a sample by radio-frequency pulses with filling frequencies equal to ω _Q + Δω _Q , ω _Q -Δω _Q.
Secondly, this method allows you to excite and observe signals with wide NQR lines.

 Thirdly, this method of exciting the echo signals allows you to observe them with maximum amplitude.

 Analysis of the distinguishing features of the present invention showed that such a method for observing quadrupole spin echo signals was not detected. He has a novelty and inventive step.

The method is implemented using a two-part pulse NQR spectrometer (AS USSR N 1132207, IPC G 01 N 24/10, 1984. Bull. N 48) with the addition of a third sensor and receiver. One channel is tuned to the frequency ω _Q + Δω _Q , and the other to the frequency ω _Q -Δω _Q , the echo signal is recorded at the frequency ω _Q , to which the third sensor and receiver are tuned.

 In FIG. 1 and 2 shows the pulse programs with which the proposed method is implemented. They differ in the excitation conditions of the echo signals.

 Let us consider in more detail two such methods for observing quadrupole spin echo signals using two-pulse excitation examples.

First, we act on a sample containing quadrupole nuclei with two RF pulses with a time interval τ between them. For a two-pulse program, two options are possible;
1. The frequency of filling the first pulse ω _Q + Δω _Q , and the second pulse ω _Q -Δω _Q , (Fig. 1).

2. The frequency of filling the first pulse ω _Q -Δω _Q , and the second pulse ω _Q + Δω _Q , (Fig. 2).

(1)
в момент времени

Если воздействовать на образец по программе на фиг.2, то наблюдается сигнал эха с амплитудой

(2)
в момент времени

Здесь (I'_x)m, m-1 - элемент матрицы оператора I_x в представлении квадрупольного гамильтониана Η_Q; являются тригонометрическими секциями угловых длительностей радиочастотных импульсов: ω_Q/- резонансная частота возбуждаемого перехода: Δω_Q - расстойка от резонансной частоты в пределах полуширины наблюдаемой линии ЯКР: τ - временной интервал между первым и вторым импульсами: m - магнитное квантовое число.If you act on the sample according to the program in FIG. 1, then an echo signal with amplitude

(1)
at time

If you act on the sample according to the program in figure 2, then there is an echo signal with amplitude

(2)
at time

Here (I ' _x ) m, m-1 is the matrix element of the operator I _x in the representation of the quadrupole Hamiltonian Η _Q ; are the trigonometric sections of the angular durations of the radio frequency pulses: ω _{Q /} is the resonance frequency of the excited transition: Δω _Q is the distance from the resonance frequency within the half-width of the observed NQR line: τ is the time interval between the first and second pulses: m is the magnetic quantum number.

 From the expressions (1) and (2) it is seen that the amplitude of the observed echo signals has not changed (as in the prototype), and the location of the signals depends on the excitation conditions (differs from the prototype).

The implementation of the invention was carried out on ⁶³ Cu in Y ₁ , Ba ₂ Cu ₃ O _7-d (d> 0) at a frequency of 31.13 MHz (T = 297 K). The width of this NQR line is ~ 200 kHz. One channel is tuned to the frequency (31.13 + 0.1) MHz, the other to the frequency (31.13 - 0.1) MHz, monitoring is carried out at a frequency of 31.13 MHz. At large values of τ, a shift is well observed (relative to Han type signals) at the locations of the echo signals.

 Thus, the present invention allows to excite and observe signals with wide NQR lines, to obtain additional information about the structure and structure of chemical compounds, the study of which was previously difficult.

Claims (2)

1. A method for observing quadrupole spin echo signals, including exposing a sample containing quadrupole nuclei to two radio frequency pulses with a time interval τ between them, recording echo signals at the resonant frequency of the excited transition, characterized in that the filling frequency of one of the pulses is set to ω _Q + Δω _Q, a pulse frequency equal to another fill ω _Q -Δω _Q, where ω _Q - resonant frequency excited transition, Δω _Q - detuning of the resonant frequency within the half-width of the observed inii NQR. 2. The method according to claim 1, characterized in that the first RF pulse with a filling frequency equal to ω _Q + Δω _{Q is} supplied, and the second RF pulse with a filling frequency equal to ω _Q -Δω _Q.
3. The method according to claim 1, characterized in that the first RF pulse with a filling frequency equal to ω _Q -Δω _{Q is} supplied, and the second RF pulse with a filling frequency equal to ω _Q + Δω _Q.

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